Migrations are ticking clocks: every day, countless animals must move or die, driven by changing seasons, and a changing climate; they are racing to reach their destination, before it's too late, to breed, feed or simply stay alive. From the ever changing Arctic ice floes to the salt pans of Botswana, trillions of creatures are compelled to journey - for the sake of their own survival and their legacy. But for animals ranging from walruses to whale sharks, zebras to orangutans, pronghorn to plankton -- every day is a race against time.